Environment Take nothing for granted
Seagrass may be all prevalent in many popular anchorages but that does not make it invincible
When a yacht drops anchor in a seagrass meadow and leaves a divot, or an outboard motor propeller makes a scar, how long does it take for the seagrass to grow back? A lot longer than you probably think. Neptune grass in the Mediterranean, turtle grass in the Caribbean and similar species around the world are the redwoods and oaks of marine ecology: they’re extremely slow- growing and can live for thousands of years. When damaged, they take decades to recover – or they might never grow back at all. However, they can be restored and 11th Hour Racing is funding some
groundbreaking work in this field. Seagrass propagates mainly by growing its rhizomes in a mat that spreads out just a few inches beneath the sea floor. If a hole is made a bit deeper than that, the seagrass can’t regrow unless the hole is filled in with sand or sediment brought by waves or currents. But quite often waves or currents can make the hole bigger. What starts as a small divot soon becomes a huge crater as the edges of the substrate under the mat of rhizomes are eroded and washed away, leaving an entire meadow of seagrass much
76 SEAHORSE
more vulnerable to the next storm. Anchors and outboard motors do a lot more damage than most sailors imagine. But a severe storm can wipe out an entire ecosystem, driving large pieces of flotsam – trees, parts of buildings, boats ripped from their moorings – across seagrass meadows, carving long, deep scars that just get bigger over time. That’s what happened in Puerto Rico in 2017 when two category five hurricanes, Irma and Maria, destroyed great swathes of seagrass and mangroves. Why should we care about marine plants and trees in the wake of a natural disaster that kills thousands of people and wrecks the homes and livelihoods of many thousands more? Because seagrass and mangroves, like salt marshes, are natural storm protection barriers that absorb huge amounts of wave energy and prevent coastal erosion. They also play a crucial role in maintaining water quality and support the lifecycle of fish species that communities and entire nations rely on for food. There’s another big-picture reason for all of us to care. While science points clearly to manmade climate change as a major cause of the increase in severe weather events
Above:
this thriving meadow of Thalassia seagrass is an extremely effective carbon sink that captures large amounts
of CO2 – up to ten-times as much per hectare as a forest on dry land – and sequesters it in the seabed. Seagrass also absorbs wave energy which helps reduce coastal
erosion and supports the lifecycles of many species including commercial fish stocks
that we’ve witnessed in our lifetimes, it also identifies coastal wetlands as one of our best solutions for confronting and curbing climate change. Together, healthy seagrass and mangroves form a ‘blue carbon’ ecosystem, also known as carbon sinks, that can store up to 10 times as much carbon per hectare as a forest on land. But the reverse is also true. When blue carbon ecosystems are degraded, they release similarly huge amounts of stored carbon back into the atmosphere – and right now, in most parts of the world, they are in sharp decline.
Slow-growing seagrasses like Thalassia (turtle grass) and Posidonia (Neptune grass) store far more blue carbon than their own weight, sequestering it in the substrate. Mangroves do the same and also store large amounts in their trunks, roots, limbs and leaves. Restoring them not only mitigates against some of the worst symptoms of climate change, like flooding and erosion, it also helps to combat the root cause. On top of all the obvious benefits for local ecosystems and communities, seagrass and mangrove restoration projects can, if done right, offer organisations
BEN SCHEELK/THE OCEAN FOUNDATION
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